We propose to continue the ongoing onco-developmental studies involving gene regulation of chicken fetal red blood cell antigens during normal development and malignancy. Objectives are to explore the hypothesis that chicken onco-development antigens represent genic products of erythroid cells which are expressed at a specific stage of cellular differentiation and to characterize the onco-developmental antigens genetically, chemically, and functionally. Immunological, serological, genetic and chemical analyses will be used to investigate the following projects: a. Detection of additional red blood cell membrane onco-developmental antigens. b. Localization of onco-developmental antigens to cell types, including erythroid precursor cells. c. Analyses of antigenic phasing with development: Resolution of one molecule with multiple antigenic determinants versus multiple molecules with one antigenic determinant. 3. Analyses of genetic transmission and genic regulation of the red blood cell antigens. e. Characterization of onco-developmental antigens by carbohydrate inhibition studies. f. Resolution of onco-developmental antigens as viral receptors. g. Location of beta-microglobulin on chicken cells with development, erythroid cellular differentiation and malignancy.